Relation of Fish Size and Growth Rate to Migration of Spring Chinook Salmon Smolts

Abstract

We examined the relation of size and growth rate to downstream migration in yearling spring chinook salmon Oncorhynchus tshawytscha. A group of juvenile chinook salmon was graded by size into small and large categories; half the fish in each category were reared at an elevated temperature beginning in mid-February, resulting in four distinct treatment groups: large–warm, large–cool, small–warm, and small–cool. Fish from warmwater treatment groups displayed significantly higher growth rates through the spring than coolwater groups. Fish were released into a natural creek on two dates (25 March, release 1 and 12 April, release 2), and downstream movement was monitored. For each release, fish that migrated past a weir within the first 5 d postrelease had significantly higher spring growth rates than fish that did not migrate within that period. A similar comparison of release length to migration demonstrated significant differences only in release 2. Also for release 2, fish from the large–warm and small–warm treatment groups were recovered in higher proportions than fish from large–cool and small–cool groups. These results indicate that fish with relatively higher spring growth rates moved downstream sooner than fish with relatively lower growth rates. Furthermore, smolt size and migration were related with larger fish moving downstream sooner than smaller fish; however, this relation was weaker than that found between growth rate and migration.

Notes

¹ Reference to trade names does not imply endorsement by the National Marine Fisheries Service.